With intravenous infusion devices, it is necessary to have a robust air detection system to protect the patient from the hazards of air emboli. Several features may be incorporated into an air detection system, allowing the system to be customized to meet the needs of different patient populations. Since air detection is one of the most frequent false alarms in infusion systems, it is necessary that infusion systems can discriminate between conditions that are clinically relevant and those that are not. Most systems employ a single bubble alarm algorithm that detects a single continuous slug of air to prevent air embolism. The ECRI Institute has stated that “We are not aware of any reports of fatal venous air embolism that (have) occurred during the use of pumps having functional air-in-line detectors. This suggests that any detector with minimum volumes within the 0.05 to 0.2 mL range provides sufficient protection from an air embolism.” A review of applicable literature confirms this volume as a general guideline to the acceptable amount of air that may safely be absorbed by the body.
Certain circumstances can arise in which a single or continuous slug of air is not present but which is determined or perceived by the clinician to represent an equivalent situation. In particular, when the medication container is emptied during an infusion program, a transition occurs from the delivery of fluid to air. The transition period may involve a mixture of air and fluid (“froth”) that does not include a single air slug of sufficient volume to trigger the single bubble alarm. Consequently, delivery of the air/fluid mixture occurs until the single bubble criteria are eventually met. However, the froth that is pumped through the IV line may be (by volume) predominantly air and may be considered by the clinician to be equivalent to a single air slug. In addition, the multitude of small air bubbles comprising froth may coalesce as the mixture approaches the IV patient access point. Consequently, the time period during which froth is pumped prior to a single bubble alarm may be viewed by the clinician as a delay in the alarm due to the observed high percentage of air in the IV infusion line.
An infusion system and method is needed which will provide an alarm trigger which is based upon the percentage of air delivered rather than being based on either a continuous air slug or on a measure of the total air volume delivered through time. This will provide early detection of an empty container condition where froth is present.